Not Applicable
Not Applicable
1. Technical Field
This invention relates in general to electronic communication devices and, more particularly, to a circuit for providing a divided quadrature signal.
2. Description of the Related Art
Wireless communications devices are continuously being updated for smaller size, greater battery life and lower cost. One important factor in achieving these goals is greater integration of the electronics used in a wireless communications device. In many devices, such as mobile phones, it is envisioned that the entire electronics will be integrated onto a single chip in the near future.
In order to achieve the highest possible level of integration, a homodyne transmitter design may be used. One of the major issues with this design is on-chip generation of quadrature signals from the transmit VCO (voltage controlled oscillator). The quadrature signals should have a very low close in phase noise as well as a very low noise floor, on the order of xe2x88x92165 dBc at a 20 MHz offset. By dividing the signal frequency in two, a 6 dB gain in close-in phase noise can be obtained. Presently, signal division is generally performed using latches to divide the signal and generate quadrature signals. Unfortunately, in using latches to produce the quadrature signals, a noise floor of xe2x88x92145 dBc is about the best that can be achieved.
Therefore, a need has arisen for a low-noise solution for generating a divided quadrature signal.
In the present invention, a quadrature divider includes a first analog mixer for receiving a digital input signal at a predetermined frequency at a first input of the first mixer and a second analog mixer for receiving the input signal with a 180xc2x0 phase shift at a first input of the second mixer. The output of the first mixer is coupled to a second input of the first mixer and an output of the second mixer is coupled to a second input of the second mixer.
The present invention provides significant advantages over the prior art. A quadrature signal at one-half of the input frequency is obtained, without the noise associated with the use of latches to obtain the divided signal. In a differential embodiment, the 180xc2x0 phase shift between inputs to the mixers can be obtained by a polarity inversion at the inputs to one of the mixers, thereby eliminating any unwanted delays associated with the phase shift.